Typical water runoff contains a surprisingly large amount of oil and other contaminants. The resulting contamination of natural receiving water incurs enormous annual costs, both financial and environmental. For example, a government study in one published article showed that storm water sampled from street sites contained an xe2x80x9cevent mean concentrationxe2x80x9d of 2.2 mg. of oil per liter of runoff water. Shepp, xe2x80x9cPetroleum Hydrocarbon Concentrations Observed in Runoff from Discrete, Urbanized Automotive-Intensive Land Uses,xe2x80x9d Watershed ""96. If one meter of rain per year falls on a street 10 meters wide, then at that observed mean rate, the annual runoff from each kilometer of street will contain about 275 liters of hydrocarbons.
Various systems have been developed to remove hydrocarbons and other chemical contaminants from runoff water. For example, U.S. Pat. No. 6,080,307, and commonly owned with the present application, discloses a system for recovering trash and oil from water passing into storm drains or the like.
Unfortunately, a report of the National Resources Defense Council (xe2x80x9cTesting the Waters 2001,xe2x80x9d available from www.nrdc.org) makes it clear that such conventional systems for chemical decontamination and debris removal are inadequate for effective purification of runoff water. Eighty-five percent of beach closings and health advisories occurring in 2000 were the result of high bacteria levels, according to the report, and xe2x80x9cpolluted runoff and storm water caused or contributed to more than 4,102 closings or advisories.xe2x80x9d Clearly there remains a need for further improvements in the purification of runoff water to alleviate continued concerns about public health.
In accordance with aspects of the present invention, including various advantageous methods, hydrophobic polymer granules or fragments employed as filter media, e.g., for filtering runoff water, include an antimicrobial compound on their surfaces. Advantageously, such polymer granules or fragments are able to reduce proliferation of microbial organisms in the water in addition to sorbing chemical contaminants from the water. (As used herein, xe2x80x9creduce proliferationxe2x80x9d includes reducing counts or concentrations of live or otherwise active microorganisms, preventing microorganisms from reproducing or otherwise proliferating, or both.) By employing this dual decontamination action, filter systems employing such particles can further improve the quality of runoff water (or other water streams) and reduce the risk presented by potentially harmful organisms in the water.
In a particularly advantageous method of the invention for preparing filtering and decontamination media, polymer granules having high sorbency for one or more predetermined contaminant liquids, such as oil or other hydrocarbons, are irrigated with a solution that contains a reactive antimicrobial compound. (As used herein, the term xe2x80x9cirrigatexe2x80x9d means applying solution to a polymer material by any suitable technique, including spraying, static immersion, centrifugal innundation, or conjoined fluid flow of particles and solution.) The polymer granules are phobic to water (i.e., hydrophobic) and to the liquid of the solution (which may itself be water) and thus do not sorb any significant quantities of the solution even during irrigation. Because the antimicrobial compound in the solution is reactive, it becomes grafted to the polymer surfaces of the granules without the solution being substantially sorbed (i.e., absorbed or adsorbed) by the granules. The resultant polymer granules are capable, upon immersion in contaminated water, of both sorbing contaminant liquids and reducing biological contamination in the water, a clearly beneficial property.
The method can also include drying (at least substantially) the solution-irrigated polymer granules and then extruding the polymer granules into fragments of filter media. Alternatively, the method can include forming unirrigated granules into fragments of filter media, such as using an extrusion process, then irrigating the formed fragments. Although many of the embodiments disclosed herein are described with reference to irrigated granules later formed into fragments, the inventor also contemplates alternatives using granules formed into fragments and then irrigated. The method can further include supporting the fragments about an open recess within a filter module. When the contaminant liquids include hydrocarbons, such a filter module is capable of both removing oil from water passing into the open recess and reducing proliferation of microbial organisms in the water. Thus, an advantageous result of the method is a further improvement in the purification of runoff water over that which is conventionally available.
A fragment of filter media according to one aspect of the invention is comprised of: a matrix of compliant, hydrophobic, olefinic polymer; an oil-sorbent, hydrophobic copolymer in the matrix; and an antimicrobial compound. The antimicrobial compound can be grafted, in one useful embodiment, e.g., by the advantageous method mentioned above, to a portion of the polymer of the matrix and to a portion of the oil-sorbent, hydrophobic copolymer in the matrix. Altermatively, the antimicrobial compound can be grafted to the copolymer alone (or, although less preferred, to the granules of the matrix alone). Consequently, the fragment is advantageously capable of both sorbing oil from surrounding water and reducing proliferation of microbial organisms in the water. (As used herein, the term xe2x80x9cparticlesxe2x80x9d refers to either granules or fragments, including granules in loose form as well as granules formed into fragments, and including fragments alone or linked to adjacent fragments to form a coherent polymer body of macroscopic dimensions.)
A filter system according to another aspect of the invention includes a multitude of irregular, macroscopic fragments of the type discussed above and a filter module that supports the fragments about an open recess. Such a filter system is highly desirable in that it can perform the dual-action decontamination of both sorbing oil, grease, etc. from water passing into the open recess and reducing proliferation of microbial organisms in the water or in residues left in (or between) the filtering fragments or the filter module.
Also highly desirable is a method of the invention for improving chemical and biological purity of water entering a storm drain. The method includes sorbing one or more targeted contaminants from the water by directing flow of the water through interstices of a multitude of irregular, macroscopic fragments that are sorbents of the contaminants, e.g., fragments of the type discussed above. In the method, the fragments include an antimicrobial compound on their surfaces, e.g., a reactive compound grafted to surfaces of polymer fragments. Proliferation of microbial organisms in water passing over those surfaces is advantageously reduced even as chemical contaminants are sorbed from the water.
These and other compositions, systems, and methods of the invention can employ particular materials according to various aspects of the invention for particularly favorable results. First, the antimicrobial compound can be an organosilane compound not susceptible to self-condensation in water, which avoids the use of more hazardous solutions. Second, the contaminant-sorbent, hydrophobic copolymer can be styrene-butadiene-styrene (SBS) or hydrogenated styrenic block copolymer (xe2x80x9cSEBSxe2x80x9d), both of which are highly oil-sorbent, non-toxic, and remain coherent after becoming oil-saturated. The compliant, hydrophobic polymer can be ethylene propylene diene monomer (EPDM) or ethylene propylene monomer (EPM), both of which permit formation of a polymer matrix that supports the oil-sorbent, hydrophobic copolymer while also absorbing a certain quantity of oil.
The above summary does not include an exhaustive list of all aspects of the present invention. Indeed, the inventor contemplates that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the detailed description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary.